Wireless communication systems are widely deployed to provide various types of communications (such as voice and data) to multiple users. Such systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), or other multiple access techniques. A wireless communication system may be designed to implement one or more standards, such as IS-95, cdma2000, IS-856, W-CDMA, TD-SCDMA, and other standards.
Presence detection and location-based services have long been sought after in wireless communications. In addition to supporting emergency services (e.g., E911 calls), wireless operators are striving to provide a wide range of new applications targeted for the everyday consumer and enterprise user, such as child locators, turn-by-turn navigation, directory services, voice concierge, roadside assistance, and many others. A challenge hence lies in providing accurate and reliable position location to enable such applications.